This invention relates to the hydrocarboxylation of olefins to form carboxylic acids. More specifically, this invention relates to the hydrocarboxylation of propylene with CO and H.sub.2 O in the liquid phase to produce butyric acid, wherein the branched or "iso" butyric acid isomer product predominates. The isobutyric acid may then be dehydrogenated to produce methacrylic acid.
Conventionally, hydrocarboxylation of olefins has been intended to produce predominantly the linear, straight-chain or normal (n) isomer of the carboxylic acid desired.
U.S. Pat. No. 3,641,074 to Fenton discloses the preparation of normal or straight chained carboxylic acids, esters and anhydrides via the carbonylation of olefins in the presence of a Group VIII noble metal in complex association with a biphyllic ligand. Suitable ligands may include triarylphosphine and triarylarsine among others.
U.S. Pat. No. 3,816,490 to Forster et al. discloses the production of carboxylic acids by carboxylation of olefins, utilizing a Group VIII metal compound, preferably cobalt, rhodium and iridium together with a phenolic promoter compound. The metal compound may be elemental metal, a simple salt, or an organometallic complex such as a phosphine. The reaction yields predominantly normal carboxylic acids when isomeric products are to be prepared.
U.S. Pat. No. 3,856,856 to Nozaki discloses the carbonylation of alcohols using platinum-promoted cobalt/iodide in catalysts which may be promoted by phosphine ligands including triphenylphosphine and substituted triphenylphosphines such as tris (4-dimethylaminophenyl) phosphine.
U.S. Pat. Nos. 3,857,900 and 3,933,919 to Wilkinson disclose hydrogenation, hydroformylation and carbonylation reactions resulting primarily in the formation of linear products when catalysts comprising platinum group metals, ligands containing nitrogen, phosphorus, arsenic or antimony; and a halogen or pseudo-halogen are utilized.
U.S. Pat. No. 3,859,319 to Mrowca discloses carboalkoxylation of unsaturates using a catalyst comprising an organophosphorus palladium halide containing bridging phosphido groups and optionally including a tin salt promoter. The catalyst includes organophosphorus ligands such as di(lower alkyl)amino phosphines. The linear product predominates using such a catalyst system, usually over 80% linear.
U.S. Pat. No. 3,887,595 to Nozaki discloses the carbonylation of olefinic compounds to yield a high ratio of straight chain to branch-chain products using catalysts comprising a zero valent palladium or platinum complex, and a triorgano phosphine ligand, R.sub.3 P. The R groups may comprise dialkylamino hydrocarbyls and dialkyl aminophenyls. An acid halide is not present in the reaction.
U.S. Pat. Nos. 3,919,272 and 3,968,133 to Knifton disclose the preparation of linear fatty acids and esters from olefins, carbon monoxide and alcohols or water in the presence of ligand-stabilized palladium halide complexes in combination with a halide salt of either tin or germanium. Ligands may include phosphines, arsines and amines among others.
The preparation of increased ratios of branched-chain or iso-carboxylic acids to straight-chain acids is described in U.S. Pat. No. 3,661,949 to Fenton. Olefins are hydrocarboxylated in the presence of a biphyllic ligand-stabilized Group VIII noble metal compound catalyst and an iron halide co-catalyst. The ligand may include arsines or phosphines.
U.S. Pat. No. 3,437,676 to Kutepow et al. discloses the carbonylation of olefins using palladium salt catalysts which may be complexed with phosphine ligands among others. Exemplified are mixed ligand systems, such as in example 82 in which the palladium dichloride catalyst is complexed with benzylamine and with triphenylphosphine. The iso/n ratio of the products described in Kutepow '676 is generally less than 2.5 to 1.
U.S. Pat. No. 3,501,518 to Kutepow et al. discloses the preparation of carboxylic acids or esters from olefins utilizing a supported or nonsupported catalyst comprising metallic palladium or a palladium chalcogenide, an acid and an organic phosphine or nitrile.
U.S. Pat. No. 3,855,307 to Rony et al. discloses multiphase catalysts comprised of a porous solid carrier upon which a liquid-phase catalyst is disposed. The catalyst may comprise metals complexed with ligands including phosphines, arsines, amines, among others, and such catalysts may be useful for hydroformylation and carbonylation reactions. The exemplified reactions demonstrate that the products obtained are predominantly composed of normal-chain hydrocarbons.
In general, the single metal salt catalyst systems are non-selective for the "iso" form of the carboxylic acid products, tending to yield either predominantly straight chain products, or a slightly favored distribution of iso-products. Any catalyst system to be utilized in the hydrocarboxylation reaction must be thermally stable at the temperatures required for the reaction to effectively occur. Other factors which effect the hydrocarboxylation reaction are the molar ratios of catalyst to stabilizing ligands, to the reactants, and to other components of the system.